Nurul Ferdous has posted his "two cents" on Doctrine - his thoughts on the good and bad things about the popular ORM tool.
What is Doctrine? Doctrine is a popular ORM for PHP which works with RDBMS via PHP objects. This is built inspired by Hibernate from JAVA. This acts as an abstraction layer between PHP and RDBMS.
In his list of good things about Doctrine are things like its hiding of business logic, automatic CRUD, automatic modification of DQL queries, migrations and unit testing interfaces. On his "bad list" are things like not being able to use foreign keys as an identifier, heavy emphasis on an "id" column, not all data types are in DBAL and the SQL constructs missing in DQL. He also includes a scenario where he definitely not use Doctrine - a specific example from a project he just worked on that pushed the limits of the tool.